A study of S-doped TiO₂ for photoelectrochemical hydrogen generation from water

Sulfur-doped titanium dioxide (TiO₂) was investigated as a potential catalyst for photoelectrochemical hydrogen generation. Three preparation techniques were used: first ballmilling sulfur powder with Degussa P25 powder (P25), second, ball milling thiourea with P25, and third a sol–gel technique involving titanium (IV) butoxide and thiourea. The resulting powders were heat-treated and thin-film electrodes were prepared. In all three cases, the heat-treated powders contained small amounts of S (1–3%). However, Rietveld analysis on X-ray diffraction (XRD) measurements revealed no significant changes in lattice parameters. For the samples prepared using thiourea, X-ray photoelectron spectroscopy (XPS) measurements indicated the presence of N and C in the heat-treated powders in addition to S. In all cases, visible-ultraviolet spectroscopy performed on bulk powders confirmed the extension of absorption into the visible region. However, the same spectroscopic technique performed on thin-film electrodes (∼0.5 μm) suggests that the absorption coefficients were very small in the visible region (≤10⁴ m⁻¹). The first and third methods yielded powders with substantially smaller photocatalytic activity relative to P25 powder in the UV region. The electrodes prepared from powders obtained using the second method yielded photocurrents comparable to those prepared from P25 powder.